##### Welcome to Subscribe On Youtube

Formatted question description: https://leetcode.ca/all/1116.html

# 1116. Print Zero Even Odd

Medium

## Description

Suppose you are given the following code:

class ZeroEvenOdd {
public ZeroEvenOdd(int n) { ... }      // constructor
public void zero(printNumber) { ... }  // only output 0's
public void even(printNumber) { ... }  // only output even numbers
public void odd(printNumber) { ... }   // only output odd numbers
}


The same instance of ZeroEvenOdd will be passed to three different threads:

1. Thread A will call zero() which should only output 0’s.
2. Thread B will call even() which should only ouput even numbers.
3. Thread C will call odd() which should only output odd numbers.

Each of the threads is given a printNumber method to output an integer. Modify the given program to output the series 010203040506... where the length of the series must be 2n.

Example 1:

Input: n = 2

Output: “0102”

Explanation: There are three threads being fired asynchronously. One of them calls zero(), the other calls even(), and the last one calls odd(). “0102” is the correct output.

Example 2:

Input: n = 5

Output: “0102030405”

## Solution

This problem can be solved using semaphores. In the class, create three semaphores semaphoreZero, semaphoreOdd and semaphoreEven for methods zero(), odd() and even() respectively. Initially, semaphoreZero has 1 permit, while semaphoreOdd and semaphoreEven has 0 permits.

For each method zero(), odd() and even(), in the loop, there are three steps. The first step is to acquire a permit from the current semaphore. The second step is to call the printNumber.accept(x) method for the current number. The third step is to release a permit back to the next semaphore.

• import java.util.concurrent.Semaphore;
import java.util.function.IntConsumer;

public class Print_Zero_Even_Odd {

public class ZeroEvenOdd {
private int n;
private Semaphore even;
private Semaphore odd;
private Semaphore zero;

public ZeroEvenOdd(int n) {
this.n = n;
even = new Semaphore(0);
odd = new Semaphore(0);
zero = new Semaphore(1);
}

// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 0; i < n; i++) {
zero.acquire();
printNumber.accept(0);
if ((i & 1) == 0) {
odd.release();
} else {
even.release();
}
}
}

public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 2; i <= n; i += 2) {
even.acquire();
printNumber.accept(i);
zero.release();
}
}

public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i += 2) {
odd.acquire();
printNumber.accept(i);
zero.release();
}
}
}
}

############

class ZeroEvenOdd {

private Semaphore zero_S;
private Semaphore odd_S;
private Semaphore even_S;
private int n;

public ZeroEvenOdd(int n) {
this.n = n;
this.zero_S = new Semaphore(1);
this.odd_S = new Semaphore(0);
this.even_S = new Semaphore(0);
}

// printNumber.accept(x) outputs "x", where x is an integer.
public void zero(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i++) {
zero_S.acquire(1);
printNumber.accept(0);
if ((i & 1) == 0) {
odd_S.release(1);
} else {
even_S.release(1);
}
}
}

public void even(IntConsumer printNumber) throws InterruptedException {
for (int i = 2; i <= n; i += 2) {
even_S.acquire(1);
printNumber.accept(i);
zero_S.release(1);
}
}

public void odd(IntConsumer printNumber) throws InterruptedException {
for (int i = 1; i <= n; i += 2) {
odd_S.acquire(1);
printNumber.accept(i);
zero_S.release(1);
}
}
}

• class ZeroEvenOdd {
private:
int n;
int flag;
mutex m1, m2, m3;

public:
ZeroEvenOdd(int n) {
this->n = n;
flag = 1; //奇偶判断
m1.lock();
m2.lock();
m3.lock();
}

// printNumber(x) outputs "x", where x is an integer.
void zero(function<void(int)> printNumber) {
m3.unlock();
for (int i = 0; i < n; i++) {
m3.lock();
printNumber(0);
if (flag == 1)
flag = 0, m2.unlock();
else
flag = 1, m1.unlock();
}
}

void odd(function<void(int)> printNumber) { //输出奇数
for (int i = 1; i <= n; i += 2) {
m2.lock();
printNumber(i);
m3.unlock();
}
}

void even(function<void(int)> printNumber) { //输出偶数
for (int i = 2; i <= n; i += 2) {
m1.lock();
printNumber(i);
m3.unlock();
}
}
};

• from threading import Semaphore

class ZeroEvenOdd:
def __init__(self, n):
self.n = n
self.z = Semaphore(1)
self.e = Semaphore(0)
self.o = Semaphore(0)

# printNumber(x) outputs "x", where x is an integer.
def zero(self, printNumber: 'Callable[[int], None]') -> None:
for i in range(self.n):
self.z.acquire()
printNumber(0)
if i % 2 == 0:
self.o.release()
else:
self.e.release()

def even(self, printNumber: 'Callable[[int], None]') -> None:
for i in range(2, self.n + 1, 2):
self.e.acquire()
printNumber(i)
self.z.release()

def odd(self, printNumber: 'Callable[[int], None]') -> None:
for i in range(1, self.n + 1, 2):
self.o.acquire()
printNumber(i)
self.z.release()